Nightwalker: The Midnight Detective

Attacks by the nightbreed, little demons that take possession of humans and consume their souls, are rather prevalent in the realm of Nightwalker. As a whole, nightbreeds (commonly referred to as "breed" in media) are typically selfish and stupid, and they motivate their human hosts to commit crimes. Due to the difficulty in identifying these breed-related crimes, a special agency called the N.O.S. has been established to look into and resolve breed-related incidents. As atonement for the sins he did early in his vampiric life, Shido, the main character of the series, decided to defend mankind against his demonic brethren. He has little memory of his life before turning into a vampire, and even his name is an alias he adopted when he moved to Japan. Shido started a one-man (plus-one-secretary) private investigation firm after settling in Japan, which he employs to seek breeds while hiding his true nature. Even Riho, a high school student whose parents were killed in a breed attack, whom Shido decided to hire as a secretary, is kept in the dark about his true identity.